It is necessary to estimate quantities of fuel injected in order to correctly identify the injection parameters of an injection system of an internal combustion engine and be able to draw conclusions about the correct functioning of the injection system. The consistent and reliable injection of a required quantity of fuel is decisive in order to meet the new European emission standards for motor vehicles. Undesired emissions from internal combustion engines are attributable in particular to the imprecise calibration of injection parameters in the area of small fuel masses.
Most motor vehicles possess a crankshaft sensor which detects the angular speed of the crankshaft. This variable provides an excellent source for obtaining dynamic variables which can be derived from individual combustions in the cylinder. Previous technical arrangements have employed a high-resolution noise measurement in the engine using one or more microphones or knock sensors. These are attached to the engine block close to the cylinder. According to a further alternative, cylinder pressures have been measured using cylinder pressure sensors. Cylinder pressure sensors can be arranged at various positions within the cylinder. The disadvantage of both these approaches however is that they are not installed as standard systems in motor vehicles and thus significantly increase the costs of manufacturing the motor vehicle.
DE 199 45 618 A1 for example discloses the use of a crankshaft sensor to enable the injection undertaken by the injection system to be derived from the speed irregularities caused by irregular combustion. DE 198 09 173 A1 discloses a timed fuel dispensing system with which small quantities of fuel are dispensed before the actual injection. With these small quantities of fuel tolerances and errors have a recognizable effect so that these can be taken into account in subsequent injection processes.
Other approaches describe the adaptation of the energy fed to the piezo-injection systems instead of the actuation time of the injection system, in order to identify and correct the injection parameters.
The disadvantage of the above methods is that they only allow the injection parameters to be checked with restricted accuracy and with a high equipment overhead.